Re: [PATCH 0/6] Symbol namespaces

From: Martijn Coenen
Date: Tue Jul 24 2018 - 04:09:56 EST

Hi Arnd,

On Mon, Jul 23, 2018 at 4:28 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> This looks nice. I don't want to overload you with additional
> requests, but it might be good to think about how this can
> be taken further, if we want to actually convert large
> parts of the kernel to it.

No worries about overloading, I'm happy with all feedback to make this better.

> I have two ideas:
> - It would be nice to have a simple mechanism in Kconfig
> to put all symbols in a module into a namespace that is
> derived from KBUILD_MODNAME, to avoid having to
> annotate every symbol separately. This could be similar
> to how we ended up dealing with EXPORT_NO_SYMBOLS
> in the linux-2.4 days, with the goal of eventually having
> a namespace for each symbol. Similarly, we could pass
> a number of default namespaces through the Makefile,
> e.g. if we have a directory that has lots of drivers that all
> import the symbols from a common subsystem module.

I'm hinging on two thoughts here; I really like it because it
obviously reduces work and makes this easier to use. On the other
hand, you now have to look in multiple places to see if a symbol is
exported to a namespace/imported from a module. Perhaps it depends on
how coarse-grained the namespaces end up being. Either way, I think it
would be pretty easy to cook up patches for this.

> - If this is possible to implement, it would be great to have
> a way to limit the globally visible symbols in a module
> to the ones that are explicitly exported even when a that
> module is built-in rather than loadable. Not sure how this
> is best done though. A couple of things can be done with
> objcopy, or possibly by reintroducing partial linking (which
> was removed not too long ago).

If I understand you correctly, this is orthogonal to symbol
namespaces, right? Though I think there is value in doing the same
thing for symbol namespaces: right now, the only way to find out if
all modules correctly import a symbol exported to a namespace is to
run an 'allmodconfig'; not having to do that would be a win. Being
able to do the same thing for the exported symbols in the global
namespace is very similar. So yeah, I think this is a good idea and
will look into this more.

Do you think these things should be a part of these series, or can it
be a follow-up?


> Arnd